Method for controlling the boost pressure on a piston internal combustion engine with a turbocharger

ABSTRACT

The invention relates to a method for controlling the boost pressure on an unsteady-running piston internal combustion engine with a turbocharger. According to the inventive method, a blow-off valve, which is connected upstream from the supercharger turbine in the exhaust gas tract, is controlled by an engine control, the position of the pedal and a boost-proportional gradient are detected by the engine control when initiating an acceleration operation and, when a predeterminable value for the boost-proportional gradient is surpassed, the blow-off valve is actuated in an opening direction in order to effect a predeterminable controlled increase of pressure.

BACKGROUND OF THE INVENTION

The piston-type internal combustion engines of motor vehicles, inparticular passenger vehicles, which are provided with a turbochargercontrolled via a blow-off valve exhibit for specific load conditions amore or less large “turbo hole,” meaning a lack of rotational moment.This turbo hole is steady in the low-speed range and unsteady followinga jump in the load. In order to keep the unsteady turbo hole small, theboost pressure control must be designed in such a way that following aload demand by the driver, the fastest possible boost-pressure buildupoccurs. As a result of the system feedback, a highly progressiveboost-pressure increase occurs. An increase in the boost pressure alsocauses an increase in the exhaust gas energy available for driving thecharging turbine. If the acceleration occurs from low gears and startingfrom low speeds, this can result in a sudden strong increase of theboost pressure and thus to a sudden increase in the rotational moment,even if the driver keeps the pedal position constant at that moment.This is not only considered uncomfortable, but with extremely highperformance vehicles can result in danger, owing to a sudden, strongacceleration or spinning of the wheels and a swerving of the vehicle.These problems cannot be solved through specifying a limit for the boostpressure in the air intake tract and a subsequent guided actuation ofthe blow-off valve. The danger and the impression of discomfort is notcaused by the high engine moment per se, but by the increase in theengine moment that is not expected by the driver as a result of thedelay.

SUMMARY OF THE INVENTION

It is therefore the object of the invention to specify a method forcontrolling the boost pressure, which makes the buildup of boostpressure more comfortable, but which also reacts quickly to sudden loaddemands.

This object is solved according to the invention with a method forcontrolling the boost pressure of a piston-type internal combustionengine with turbocharger. With this method, a blow-off valve installedin the exhaust gas tract upstream of a charging turbine is controlled byan engine control, which also detects the pedal position and aload-proportional gradient in the event that an acceleration action isinitiated. If a predetermined value for the load-proportional gradientis exceeded, the blow-off valve is actuated in an opening direction suchthat a predetermined controlled pressure increase occurs.

Any measured value of the piston-type internal combustion engine, whichis detected in dependence on the time and permits a statement on thechange in the respective load condition of the engine in the broadestpossible sense, is considered a “load-proportional gradient” within themeaning of the invention. These measured values primarily include thetime-dependent change in the boost pressure in the air intake tract, thetime-dependent change in the air mass flow or a directly or indirectlydetermined engine moment. It is also possible to predetermine a modelvalue that is formed from measuring and control variables in the enginecontrol for a time-dependent detection of the engine load.

In addition to specifying an absolute value of the measured value thatis intended with the existing control, the measure according to theinvention consists in detecting the gradient for this load-proportionalmeasured value, meaning its change per time unit, and in specifying alimit value for this load-proportional gradient. In the even that thelimit value is exceeded, the control returns the detectedload-proportional gradient to the predetermined limit value by adjustingthe blow-off valve in the “open” direction and, depending on the designof the complete system, by also reducing the load control of the engine.The load control intervention can be effected, for example, by adjustingthe throttle valve, but also with unconventional methods such asvariable valve control times or a mixture control.

As a result, the driver can adequately react to the strong increase inthe boost pressure, which results in an increase in the rotationalmoment of the engine. It is thus avoided that the driver is surprised byan excessively rapid increase in the boost pressure. The rapid increasecauses an undesirably high pressure in the air intake tract during thedriver reaction time and thus a power output that is not desired orexpected by the driver and results, for example, in a spinning of thedrive wheels or a forward jump of the vehicle. The driver is given theopportunity to react to the increase in the engine moment with areduction in the pedal load or even through dynamic driving actions(counter steering).

The operating conditions of the piston-type internal combustion engineand the turbocharger of a motor vehicle change according to specificrules because of the unsteady operation as well as the existence of thegearshift. Thus, it is provided according to one advantageous embodimentof the invention that the respectively predetermined limit values forthe load-proportional gradient are taken from a performancecharacteristic of the engine control. For example, if the pedal is fullydepressed at low speeds and in a low gear for an acceleration operation,other values result for the turbocharger behavior and thus also for therotational moment change of the piston-type internal combustion enginethan if this action occurs at a higher speed with a different gear. Thesame is true for the effect of these changes on the comfort perceptionof the driver. These differences are taken into account by specifyingcorresponding performance characteristics in the engine control.

According to one embodiment of the invention, the pedal gradient isfurthermore taken into account as a limit value for theload-proportional gradient. The term “pedal gradient” within the meaningof the invention relates to the change in the pedal position independence on the time. Thus, if the driver pushes down the pedal onlyslowly to increase the vehicle speed, or keeps it at a constantposition, the driver expects only a slow change in the engine moment andthe limit value selected for the load-proportional gradient must besmall. If the pedal is pushed down rapidly, the driver expects acorrespondingly rapid change in the engine moment. A largeload-proportional gradient can be permitted without loss of comfort orsafety.

According to another advantageous embodiment of the invention, therespective limit value is taken from the performance characteristic forthe pedal gradient that is low-pass filtered in a negative direction.This link favorably takes into account the expectations of the driver.With a constant pedal value, meaning the pedal gradient is zero, thedriver normally expects only a moderate change in the rotational moment,even if the pedal value is high. In contrast, if the pedal is pusheddown quickly, the driver expects a rapid rotational moment increase thatcorresponds to the speed of the pedal movement. However, this increaseis less and less the farther back the pedal movement for accelerationoccurred. As a result of the low-pass filter for the signal “pedalgradient,” the pressure increase in the air intake tract that ispermitted by the engine control with increasing passage of time betweenthe signal and the response of the turbocharger is lower than wouldactually be possible. As a result, it is avoided that the driver issurprised by an unexpected, sudden increase in the rotational moment.This value can be modified further in dependence on additional inputvariables.

According to another advantageous embodiment of the invention, the boostpressure gradient in the air intake tract is detected as theload-proportional gradient. The air mass flow in the air intake tract isproportional to the pressure in the air intake tract and alsoproportional to the load. As a result, the boost pressure gradientrepresents a load-proportional gradient that is directly connected tothe respective control and regulation actions. If the driver demands astrong acceleration via the pedal position, then the increased fuelsupply causes the piston-type internal combustion engine to react byincreasing the exhaust-gas energy, which leads to an increase in theboost pressure via the charging turbine and the charger. By detectingthe boost pressure gradients, the time curve for the boost pressureincrease can be detected and, in case of an undesirably steep increase,the blow-off valve can be adjusted practically extrapolating in theopening direction, so that the increase will become less steep. As aresult of the control behavior of the complete system involving thepiston-type internal combustion engine and the turbocharger, acorresponding performance characteristic can be provided for therespective load condition and operating condition in the engine control.Thus, if the limit value for the boost pressure gradient that isrespectively specified by the performance characteristic is reached, theblow-off valve can be correspondingly opened and the energy supply tothe charge turbine can be reduced. It is thus possible to have asensitive guidance of the boost pressure increase in the air intaketract. In driving situations where the pedal movement leads to theassumption that the driver desires and expects this, the physicallypossible unsteady performance of the system can be demanded. Insituations where it can be assumed that the driver does not expectconsiderable changes in the rotational moment, the system dynamic can besuppressed to a comfortable and secure measure.

The method according to the invention and the above-discussedembodiments in principle can be used for piston-type internal combustionengines with a choke-free load control as well as a load controleffected by a throttle valve in the air intake tract. According toanother embodiment of the inventive method, the respective throttlevalve position is detected with a control effective via a throttle valveand, if the predetermined value for the boost pressure gradient isexceeded, the throttle valve is adjusted at least at times in theclosing direction. A boost pressure increase, which cannot be preventedby adjusting the blow-off valve due to the long idle times of the“blow-off valve/turbocharger” system, can thus be caught with thiscontrol action in the air intake tract. An undesirably steep increase inthe engine load can therefore still be avoided and the response time ofthe system can be shortened noticeably. An undesirably rapid increase inthe boost pressure is “caught” in the air intake tract already and asudden rapid increase in the boost pressure is avoided even with adesired strong acceleration. For a piston-type internal combustionengine with a choke-free load control, e.g., via variably controlledcylinder valves, the undesirable boost pressure increase iscorrespondingly “caught” by changing the valve control times via theengine control.

The invention is explained in further detail with the aid of schematicdrawings:

FIG. 1 is a block diagram of a piston-type internal combustion enginewith turbo charge control.

FIG. 2 illustrates the link according to the method between a low-passfiltered pedal gradient and the boost pressure gradients.

DETAILED DESCRIPTION OF THE INVENTION

The block diagram in FIG. 1 shows a piston-type internal combustionengine 1, with associated turbocharger 2 for increasing the boostpressure of the combustion air, connected via its exhaust gas tract 3 tothe charge turbine 4 of the turbocharger 2. A controllable blow-offvalve 5 is arranged in the exhaust gas tract 3, upstream of the chargeturbine 4.

The piston-type internal combustion engine 1 with its air intake tract 6is furthermore connected to the compressor 7 of the turbocharger 2. Theexemplary embodiment shown herein is a choke-controlled piston-typeinternal combustion engine with a controllable throttle valve 8,arranged in the air intake tract 6, on the pressure side of the charger7. As shown schematically with this example, fuel is supplied viacontrollable injection nozzles 9 to the individual air intake channelsleading to the cylinders. The method described in further detail in thefollowing can be used for any type of fuel supply, meaning also for thedirect fuel injection.

The piston-type internal combustion engine 1 is provided with a motorcontrol 10, to which all measured values relevant for the engineoperation are supplied. All signals necessary for the engine operationare emitted by this motor control following a corresponding processing.However, for the following representation of the mode of operation forthe piston-type internal combustion engine with control, the control andregulation actions required for the normal piston-type internalcombustion engine operation are presumed known and are not describedherein. Described in the following are only those control and regulationconnections, which are required for realizing the method according tothe invention.

The block diagram separately shows all elements assigned per se to themotor control 10, which are used for detecting and converting themeasured values necessary for realizing the method.

With the exemplary embodiment shown herein, the boost pressure gradientis detected as the load-proportional gradient. A pressure transducer 11is arranged for this in the air intake tract 6. The value measured bythis pressure transducer is detected in a computer unit 12 as anabsolute value and, following differentiation as the boost pressuregradient dp/dt, wherein both values are made available as separatevalues to the engine control 10.

The throttle valve 8 with associated adjustment drive furthermore isprovided with a transmitter 8.1 for detecting the respective throttlevalve position α. In the same way as for the boost pressure detection, acorresponding computer unit 13 is used to determine the absolute valueof the respective throttle valve position and, through differentiation,also the throttle valve gradient dα/dt. These two values are alsoavailable to the engine control as separate values.

The desired load is fed to the engine control via a pedal 14. With theaid of a corresponding unit 15, the pedal 19 transmits the actual pedalposition φ as well as the change over time of the pedal position,meaning the pedal gradient dφ/dt, as an input value to the enginecontrol. The value of the pedal gradient is also taken into account bymeans of a low pass 16 that is assigned to the engine control 10.

With the exemplary embodiment shown herein, the crankshaft speed of thepiston-type internal combustion engine 1 is normally detected via atransmitter 17 and is made available to the engine control 10.

As explained with the aid of FIG. 1, the desired values for the boostpressure and the fuel injection are adjusted to “full load” via theengine control 10 if the pedal 14 is depressed strongly in a low gear.The throttle valve 8 accordingly is opened fully and the amount of fuelinjected is increased. Thus, an increased energy amount from the exhaustgas tract 3 is available with the aforementioned delay at the chargeturbine 4 that leads to an increase in the boost pressure of the intaketract, which is desired per se. However, since the exhaust gas energyand thus also the boost pressure in the air intake tract 6 increasefaster with a corresponding load demand by the pedal 14, e.g. a fasterpedal movement, than is good for the operation of the piston-typeinternal combustion engine and the connected vehicle, the pressure, inparticular the boost pressure gradient dp/dt, is detected via thepressure transducer 11. This value is converted in the engine control 10to an adjustment signal, following a balancing with a value stored in aperformance characteristic 18 as limit value for the boost pressuregradient. The engine control will open the blow-off valve 5 and, ifnecessary, push back the throttle valve 8 at least briefly by a slightmeasure in closing direction. Thus, an excessive boost pressure increaseis “caught” if the actual boost pressure gradient has reached a limitvalue taken from the performance characteristic for the respectiveoperating condition. The “exhaust gas energy supply” for the chargeturbine is taken back and, if necessary, the “air supply” for thepiston-type internal combustion engine reduced further by throttling theair flow. This results in a guided increase in the boost pressure, asexplained in further detail with the aid of FIG. 2, diagram II, curvese₁ and f₁.

For this, the blow-off valve 5 is returned to the position predeterminedby the engine control and assigned to the pedal value, in accordancewith the predetermined values from the performance characteristic 18, soas to achieve the desired steady end pressure.

The throttle valve 8 with its actuation, shown in the block diagram, isomitted for a throttle-free piston-type internal combustion enginecontrol since the cylinder valves are actuated via fully variablycontrolled valve drives, for example electromagnetic actuators that arecontrolled directly by the engine control 10. By influencing theopening, moments, but also the opening length for the cylinder valves,the piston-type internal combustion engine load can be controlled in thesame way as with a throttle valve.

A rapid actuation of the pedal 14 in a low gear and at a low speed inthis case also results in the previously described effect of a delayed“start-up” of the turbocharger and a progressive increase of the boostpressure in the air intake tract 2. The pressure increase in the airintake tract leads to a correspondingly higher cylinder filling withotherwise identical actuation of the valve play for the cylinder valves.Thus, even with a piston-type internal combustion engine that is notcontrolled by a throttle, the previously described danger of a suddenincrease in the rotational moment can occur.

Even with a throttle free control of a piston-type internal combustionengine, it is possible to additionally react to the strong increase inthe boost pressure in the air intake tract by detecting the boostpressure gradient via the pressure transducer 11 in the air intake tract6. This is true through actuating the blow-off valve 5 as well aschanging the valve control times for the gas intake valves. Thus, theboost pressure is increased only based on the predetermined values fromthe performance characteristic.

FIG. 2 shows the preferred embodiment of the method for two differentload conditions, with the link between the detection of a low-passfiltered pedal gradient and the detection of the respectively associatedboost pressure gradient according to the method. The diagram I in FIG. 2shows the percentage course of the pedal value with the curve a and,identically, the value of the connected throttle valve position. For anacceleration operation at moment t₀, the driver depresses the pedal 14fully over a short period of time, so that the pedal 14 is held in thefull gas position.

The curve b shows the associated pedal gradient. The pedal gradientexperiences a steep increase, as shown in curve b, because it takes onlya very short time to traverse the pedal angle from the pedal startingposition at t₀ to the end position at time t₁. The increase drops backimmediately to “zero” as soon as the pedal end position and thus the endof the pedal movement is reached. This pedal gradient is detected viathe engine control 10, as described further in the following, and isstored as a measured value. The measured value is present as a low-passfiltered signal at the engine control, as shown with curve c, so thatstarting with the original, large pedal gradient, the value decreaseswith increasing time and a change in the predetermined limit value ispossible for the load-proportional gradient.

The associated diagram II shows the course over time of the pressureinside the air intake tract 6. If the pedal is moved rapidly to thefull-load position at point in time t₀, corresponding to curve a indiagram I, then the desired value according to curve d for the full-loadoperation is specified for the engine control as the boost pressure inthe air intake tract. Owing to the fact that the pressure increase for aturbocharger with speed increase for the charger is initially low, asopposed to a mechanical charger, but then increases quite progressively,the pressure increases correspondingly depending on the load case.

The pressure increase initially is linear until the environmentalpressure p_(u) is reached. Following this, another pressure increaseoccurs in the intake system through a running up OF the turbocharger,which change occurs rapidly in a first load case. Thus, the boostpressure quickly increases further. For a conventional control accordingto the curve branch e₂, this increase is very steep in the last sectionbefore reaching the desired pressure. A strongly delayed response of theturbocharger is shown for the second load case. In that case, thefurther pressure increase is delayed, without action according to thedescribed method, but then rises steeply according to curve f₂ as aresult of the system feedback.

This increase in dependence on the time can be detected as the gradient.

A maximum permissible boost pressure gradient, represented by the riseof the dashed curve branches e₁and f₁, is specified via a performancecharacteristic stored in the engine control, as described in the above.If the rise in curves e and f)f₁ reaches the limit value, represented bypoint in time t₁ or t₃, then a corresponding actuation of the blow-offvalve and/or the throttle valve according to the described method isused to sufficiently counteract the boost pressure increase. Thisresults in a guided boost pressure course according to the curve branche₁ and f₁.

A different limit value can be selected for the load case “e” than forthe load case “f,” owing to the change in the predetermined limit valuefor the boost pressure gradient or in general the load-proportionalgradient and the measurable value for the filtered pedal gradient. Forthe load case “e,” only a low damping of the dynamic is required sincethe driver at point in time t₁ still expects an increase in therotational moment as a result of the fact that the pedal was depressedcompletely only a short time before. In particular, the driver demandsthis from the engine via the pedal. In the case “f,” the driver alsodemands the full-load rotational moment, but the engine cannot meet thisrequirement until the point in time t₃ owing to the inertia of thephysical system. By influencing the blow-off valve and/or the throttlevalve, it is prevented that the driver is surprised at point in time t₃by an increase in the rotational moment that is no longer expected atthis level.

What is claimed is:
 1. A method for controlling the boost pressure in anunsteadily operated piston-type internal combustion engine with aturbocharger, for which a blow-off valve is installed in the exhaust gastract upstream of a charge turbine and is controlled via an enginecontrol, said method including: once an acceleration operation isinitiated, detecting, by the engine control, a pedal position and aload-proportional gradient and, once a predetermined value for theload-proportional gradient is exceeded, actuating the blow-off valve inan opening direction such that a predetermined, controlled pressureincrease occurs; and further including taking the pedal gradient intoaccount for the limit value specified for the load-proportionalgradient.
 2. A method for controlling the boost pressure in anunsteadily operated piston-type internal combustion engine with aturbocharger, for which a blow-off valve is installed in the exhaust gastract upstream of a charge turbine and is controlled via an enginecontrol, said method including: once an acceleration operation isinitiated, detecting, by the engine control, a pedal position and aload-proportional gradient and, once a predetermined value for theload-proportional gradient is exceeded, actuating the blow-off valve inan opening direction such that a predetermined, controlled pressureincrease occurs; and further including taking the respective limit valueof the load-proportional gradient from the performance characteristicvia the pedal gradient that is low-pass filtered in negative direction.3. A method for controlling the boost pressure in an unsteadily operatedpiston-type internal combustion engine with a turbocharger, for which ablow-off valve is installed in the exhaust gas tract upstream of acharge turbine and is controlled via an engine control, said methodincluding: once an acceleration operation is initiated, detecting, bythe engine control, a pedal position and a load-proportional gradientand, once a predetermined value for the load-proportional gradient isexceeded, actuating the blow-off valve in an opening direction such thata predetermined, controlled pressure increase occurs; and wherein: thepiston type internal combustion is a piston-type internal combustionengine with a load control effected via a throttle valve in the airintake tract; and the method further includes detecting the respectivethrottle valve position and upon exceeding the predetermined value forthe boost pressure gradient, displacing the throttle valve in a closingdirection, at least at times.
 4. A method according to claim 3, whereinthe respectively predetermined limit value for the load-proportionalgradient is taken from a performance characteristic of the enginecontrol.
 5. A method according to claim 3, wherein the boost pressuregradient in the air intake tract is detected as the load-proportionalgradient.
 6. A method for controlling the boost pressure in anunsteadily operated piston-type internal combustion engine with aturbocharger, for which a blow-off valve is installed in the exhaust gastract upstream of a charge turbine and is controlled via an enginecontrol, said method including: once an acceleration operation isinitiated, detecting, by the engine control, a pedal position and aload-proportional gradient and, once a predetermined value for theload-proportional gradient is exceeded, actuating the blow-off valve inan opening direction such that a predetermined, controlled pressureincrease occurs; and wherein: the piston type internal combustion is apiston-type internal combustion engine with a load control effected viavariably actuated cylinder valves; and the method further includes uponexceeding the predetermined value for the load-proportional gradient,resetting the valve control times to reduced load, at least at times. 7.A method according to claim 6, wherein the respectively predeterminedlimit value for the load-proportional gradient is taken from aperformance characteristic of the engine control.
 8. A method accordingto claim 6, wherein the boost pressure gradient in the air intake tractis detected as the load-proportional gradient.